Refrigeration compressors generally comprise, in the interior of a shell, a motor-compressor assembly having a cylinder block within which is defined a cylinder having an end closed by a cylinder head defining therewithin a housing for adaptation of a suction muffler, and a discharge chamber in selective fluid communication with a compression chamber defined inside the cylinder and which is closed by a valve plate provided between the closed end of the cylinder and the cylinder head, said fluid communication being defined through suction and discharge orifices provided in said valve plate and which are selectively and respectively closed by suction and discharge valves generally carried by the valve plate.
Contiguously to such orifices there are mounted noise mufflers upstream the suction orifice and downstream the discharge orifice. In order to maintain a good thermal insulation between the relatively cold gas that is drawn and the other components adjacent to the suction muffler, the latter is generally constructed in plastic material. Thus, the overheating of the gas which is drawn along the path from the compressor inlet to the suction orifice is minimized, resulting in better volumetric yield, thereby optimizing the performance in terms of efficiency and pumping capacity (mass flow).
The cylinder head usually defines a first element of the compressor discharge muffler and it is usually constructed in metallic material so as to resist the pressure differences to which it is submitted, since its internal face is exposed to the discharge pressure and its external face to the suction pressure.
Since the suction and discharge orifices for the admission and discharge of gas in relation to the cylinder are normally close to each other, having their spatial distribution usually limited to be contained in the valve plate in the region in which it covers the cylinder, the elements that cover them (suction chamber and cylinder head) present a contiguous section. The negative effect of such proximity is that the cylinder head is the warmest point of the compressor and the heat generated thereby is thus easily transmitted to the suction chamber and therefrom to the gas to be drawn by the cylinder. This results in higher overheating of said gas and reduction of yield and capacity, as explained above.
A known project solution which is normally adopted to define the channels leading to both the suction orifice and the discharge orifice is to make the suction chamber discharge the gas flow in a volume defined by a cavity in the cylinder head and valve plate, as illustrated in FIG. 2. This construction presents the advantage of being relatively simple to manufacture, requiring components of little geometrical complexity and resulting in a structurally rigid cylinder head, which is very interesting when the working fluid causes great pressure differences and/or the size of this cylinder head is relatively large. On the other hand, there is a metallic interface separating the suction valve antechamber containing a relatively cold gas (desired to be maintained) from the cylinder discharge chamber containing hot gas. Thus, there is an intense heat transfer between both chambers, negatively influencing the performance. Furthermore, the mounting process of the suction muffler in the cylinder head requires the inclusion of relatively complex fixation elements, such as threads, or the inclusion of intermediary elements, such as a metallic suction tube, since the material (plastic) of the suction muffler tends to deform with time when submitted to temperatures which in certain cases occur in this region of the compressor, not guaranteeing the necessary reliability in the fixation of the suction muffler to the cylinder head. Moreover, to guarantee a perfect sealing between the elements, additional elements, such as o'rings or gaskets, are usually included to prevent eventual leakages from impairing the attenuation of noise, which is the main function of the suction muffler.
FIGS. 3-4 illustrate another prior art construction for the suction system which avoids the problems mentioned above. In this construction, the suction tube is constructed in plastic material and seated on the valve plate externally to the cylinder head, i.e., the suction tube is not disposed through the interior of the cylinder head, which maintains it spaced from the warmest region of the discharge chamber. In this construction, the temperatures to which the suction tube is submitted are considerably lower than those in the construction described above, thus avoiding the use of intermediary fixation elements of said prior art construction. Furthermore, the need for additional sealing elements is eliminated, since said sealing occurs in the interface between the suction tube and the gasket seated against the valve plate.
However, the disadvantage of this solution resides in the reduction of the structural rigidity of the cylinder head. In compressors that work with fluids which cause great pressure differences between the suction and discharge sides, or in compressors that have larger dimensions, deformations may occur in the cylinder head and cause leakages, impairing the performance, or ruptures in the gasket, making the compressor lose its functional characteristics. Moreover, this prior art solution further allows the occurrence of deformations as a function of the load imposed by the fixation elements (generally screws) of the cylinder head to the cylinder block,
A way to overcome the deficiency of structural fragility of this known prior art solution would be the use of materials with a higher modulus of elasticity, but which has the disadvantage of increasing the cost of the component, whether by using a nobler material, or materials that need more complex manufacturing processes.